Pol Ravigneaux was the inventor of a multitude of gearing arrangements. In many of these arrangements, which today bear his name, a pair of sun gears and a pair of ring gears are utilized with two sets of intermeshing planet gears disposed in a common carrier. The planetary gear members are sized such that a long pinion and short pinion are utilized. The long pinion extends from meshing with a respective sun and/or ring gear to mesh with the short pinion which, in turn, meshes with a sun and/or ring gear. The Ravigneaux gear sets have been utilized with one sun gear, two ring gears and the meshing pinions, or two sun gears with meshing pinions and one ring gear, and various combinations of the ring gear/sun gear elements.
Generally, the extended pinion gear is disposed radially between the opposite sun and ring gears, since it must mesh with the short pinion. The extended portion of this ring gear must be sized diameterwise to avoid contact with both the sun gear and ring which mesh with the short pinion. They must also avoid contact with any other planet pinions which might be disposed within the gear arrangement. This restricts the allowable gear sizes and ratios that might be otherwise used with the Ravigneaux gear set.
Another restriction to the gear size and overall gear ratios, is the requirement of carrier stiffness. The carrier must provide side plates and pinion pins which will be sufficiently stiff to support the loads imposed thereon by the pinion gears during torque transmission between the input and output members of the gear set.
In Ravigneaux gear sets, the end faces, side plates or cheeks of the carrier, are joined by the pinion pins which are secured therebetween. The cross-sectional area of the pinion pins is limited to the available space between the side plates which is not occupied by the planet gears. Since the Ravigneaux carrier has to enclose two sets of planet gears, the space available for posts is limited and the carrier stiffness is, as a result, also limited.